Project Abstract Alzheimer's disease (AD) is a complex multi-factorial disease involving both genetic and environmental factors. Increasingly, pathologies driven by multiple cellular components of the brain have been the focus of studies including neuronal, astroglial, microglial/immune, and endothelial/vascular cells. NO signaling is ubiquitous and has been demonstrated to be a contributor to many systemic pathologies. In the brain, NO can be generated by cell autonomous mechanisms in neurons, astroglial, microglial, and endothelial cells, and contributes to signaling pathways including those dependent on cGMP production and those post-translational modifications dependent on S- and N-nitrosylation. Our current funded study (DK102641) focuses on the role of ASL beyond its known function in ureagenesis (i.e., NO synthesis) that was prompted by the complex natural history of ASL-deficient (ASLD) patients. This includes neurocognitive delay/neurodegeneration independent of recurrent hyperammonemia, hepatic disease, and systemic hypertension. ASL is the only mammalian enzyme that can synthesize L-arginine, the sole substrate for NO synthesis by nitric oxide synthases (NOS). ASL serves distinct catalytic vs. structural functions that provide a structural model for understanding why ASLD patients defy the arginine paradox, i.e., they are unable to generate NO efficiently in spite of supplemental arginine therapy. Hence, deletion of Asl in any cell abolishes cell autonomous NO production from that cell. In this administrative supplement application, we propose to apply cell type specific deletion of Asl to probe the role of cell autonomous production of NO in neurons, microglial cells, and cerebrovascular endothelial cells in pathogenesis and progression of AD in two mouse genetic models focused respectively on APP/Ab production (5XFAD Tg6799) and tau hyper-phosphorylation (PS19). In so doing, we will not only provide a refined analysis of NO contribution to AD pathogenesis, but also identify potential targets for manipulating NO status as an approach to AD treatment.